Optical fiber ribbon and optical fiber cable housing optical fiber ribbon

ABSTRACT

Provided is an optical fiber ribbon capable of achieving higher density and reduction in diameter and accurately placing optical fibers in V-shape grooves in a fusion machine without failure. The optical fiber ribbon  1  includes three or more of optical fibers  2  arranged in parallel and connecting portions  3  connecting adjacent two optical fibers  2  together, the connecting portions  3  being intermittently provided in each of a ribbon longitudinal direction and a ribbon width direction. The connecting portions  3  are each formed in such a manner as to fill resin into a gap S formed between adjacent two optical fibers  2 , and both surfaces of the respective connecting portions  3  are each formed into a recess having a concave shape curved toward a center of the gap S to separate from lines  4,5  each connecting contact points of the optical fibers  2  when being placed on a horizontal surface.

CROSS-REFERENCE TO RELATED APPLICATION

The application is a Continuation of PCT Application No.PCT/JP2012/076590, filed on Oct. 15, 2012, and claims the benefit ofpriority from the prior Japanese Patent Application No. 2011-229066,filed on Oct. 18, 2011, the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an optical fiber ribbon having anintermittent fixing structure in which adjacent optical fibers areintermittently connected together via connecting portions, and relatesto an optical fiber cable housing the optical fiber ribbon.

There has been an increased demand for higher density and reduction indiameter in the technical field of optical fiber cables. As an exampleof a method for achieving higher density and reduction in diameter,there is proposed a method for reducing the outer diameter of opticalfibers from 250 μm, which is a presently-used size, to 200 μm or smaller(for example, described in Japanese Patent No. 3058203 (PatentLiterature 1). An optical fiber ribbon using this method has a structurein which a plurality of optical fibers each having the outer diameter of200 μm or smaller are arranged in parallel, and the entire circumferenceof the optical fibers is covered with ultraviolet curable resin.

With the optical fiber ribbon described in Patent Literature 1, however,an intermediate branching operation is difficult when laying opticalfibers into residences of subscribers. In order to lay the opticalfibers into the residences of subscribers, a cover layer entirelycovered with the ultraviolet curable resin is required to be removed inthe middle of the cable so that particular optical fibers are onlyextracted from the plurality of optical fibers. Since the entirecircumference of the plural optical fibers is covered with theultraviolet curable resin, the removal of the ultraviolet curable resinis difficult and the particular optical fibers are not easily removedfrom the other optical fibers. Further, in the optical fiber ribbondescribed in Patent Literature 1, the entirely-covered cover layerincreases the thickness of the optical fiber ribbon by the thickness ofthe cover layer, which decreases the packaging density thereof.

Japanese Patent No. 4143651 (Patent Literature 2) teaches an opticalfiber ribbon capable of solving these problems. This optical fiberribbon does not have a structure in which optical fibers are entirelycovered with resin, but has an intermittent fixing structure in whichadjacent two optical fibers of three or more of optical fibers arrangedin parallel are connected together with resin. The intermittent fixingstructure of the optical fiber ribbon described in Patent Literature 2contributes to easy intermediate branching operation and has theadvantage of higher density since the number of connecting portions issmaller than that in the structure of Patent Literature 1.

SUMMARY

However, when the optical fiber ribbon described in Patent Literature 1is fused and connected with another optical fiber ribbon, bare opticalfibers (glass optical fibers) from which the cover layer made of resinis removed may be hard to be set in a fusion machine having pluralV-shaped grooves formed at a predetermined pitch to be independentlyplaced in the V-shaped grooves. Failure in placing the optical fibers inthe V-shaped grooves in the fusion machine requires extra work toforcibly place the optical fibers in the V-shaped grooves.

An object of the present invention is to provide an optical fiber ribboncapable of achieving higher density and reduction in diameter andaccurately placing optical fibers in V-shape grooves in a fusion machinewithout failure, and provide an optical fiber cable housing the opticalfiber ribbon.

Claim 1 recites an optical fiber ribbon comprising three or more ofoptical fibers arranged in parallel and connecting portions connectingadjacent two optical fibers together, the connecting portions beingintermittently provided in each of a ribbon longitudinal direction and aribbon width direction, wherein a gap is formed between adjacent twooptical fibers, the connecting portions are each formed in such a manneras to fill resin into the gap, and both surfaces of the respectiveconnecting portions are each formed into a recess having a concave shapecurved toward a center of the gap to separate from lines each connectingcontact points of the optical fibers when being placed on a horizontalsurface.

Claim 2 recites the optical fiber ribbon according to claim 1, whereinan outer diameter dimension of the optical fibers is set to smaller thanor equal to 220 μm, and a distance between centers of the adjacent twooptical fibers is set to 250 μm, with a margin of plus or minus 30 μm.

Claim 3 recites the optical fiber ribbon according to claim 1, whereinan outermost layer of the respective optical fibers is colored.

Claim 4 recites an optical fiber cable housing the optical fiber ribbonaccording to claim 1 therein.

Claim 5 recites an optical fiber ribbon comprising three or more ofoptical fibers arranged in parallel and connecting portions connectingadjacent two optical fibers together, the connecting portions beingintermittently provided in each of a ribbon longitudinal direction and aribbon width direction, wherein a gap if formed between adjacent twooptical fibers, the connecting portions are each formed in such a manneras to fill resin into the gap and cover a periphery of the respectiveoptical fibers with the resin, and both surfaces of the respectiveconnecting portions are each formed into a recess having a concave shapecurved toward a center of the gap to separate from lines each connectingcontact points of the optical fibers when being placed on a horizontalsurface.

Claim 6 recites the optical fiber ribbon according to claim 5, whereinan outer diameter dimension of the optical fibers is set to smaller thanor equal to 220 μm, and a distance between centers of the adjacent twooptical fibers is set to 250 μm with a margin of plus or minus 30 μm.

Claim 7 recites the optical fiber ribbon according to claim 5, wherein aresin thickness of the periphery covered with the resin is set tosmaller than or equal to 15 μm.

Claim 8 recites the optical fiber ribbon according to any one of claim5, wherein an outermost layer of the respective optical fibers iscolored.

According to the present invention, a reduction in diameter of theoptical fibers is achieved and the optical fiber ribbon is easily bentdue to the intermittent fixing structure thereof in which the connectingportions for connecting adjacent two optical fibers are intermittentlyprovided in each of the ribbon longitudinal direction and the ribbonwidth direction and due to the reduced outer diameter dimension of theoptical fibers which is set to smaller than or equal to 220 μm. As aresult, a larger number of the optical fiber ribbons can be housed inthe cable so as to improve the packaging density.

According to the present invention, the distance between the centers ofadjacent two optical fibers is set to 250±30 μm, which is equal to adistance between the centers of adjacent two optical fibers of anoptical fiber ribbon commonly distributed, so as to accurately place therespective optical fibers in the corresponding V-shape grooves in thefusion machine without falling out of the V-shaped grooves.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top perspective view showing an example of an optical fiberribbon having an intermittent fixing structure according to the presentembodiment.

FIG. 2 is an enlarged cross-sectional view of a connecting portion ofthe optical fiber ribbon of FIG. 1. FIG. 2(A) is a structural example ofthe connecting portion, and FIG. 2(B) is another structural example ofthe connecting portion.

FIG. 3 is an enlarged cross-sectional view of a connecting portion ofthe optical fiber ribbon having another structure of FIG. 1. FIG. 3(A)is a structural example of the connecting portion, and FIG. 3(B) isanother structural example of the connecting portion.

FIG. 4 is a view showing a state where glass optical fibers in theoptical fiber ribbon according to the present embodiment from whichcovering is removed, are placed in V-shaped grooves of a fusion machine.

FIG. 5 is a cross-sectional view of a center tube-type optical fibercable housing the optical fiber ribbon according to the presentembodiment therein.

FIG. 6 is a cross-sectional view of an SZ-slotted optical fiber cablehousing the optical fiber ribbon according to the present embodimenttherein.

FIG. 7 is a cross-sectional view of a C-slotted optical fiber cablehousing the optical fiber ribbon according to the present embodimenttherein.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a specific embodiment of the present invention will beexplained in detail with reference to the drawings.

FIG. 1 shows an example of an optical fiber ribbon having anintermittent fixing structure according to the present embodiment, andFIG. 2 shows an enlarged cross section of a connecting portion of theoptical fiber ribbon of FIG. 1. As shown in FIG. 1, the optical fiberribbon 1 according to the present embodiment has a structure in whichthree or more of optical fibers 2 are arranged in parallel, the adjacenttwo optical fibers 2 are connected together via connecting portions 3,and the connecting portions 3 are intermittently located in each of aribbon longitudinal direction (in the X-arrow direction in FIG. 1) and aribbon width direction (in the Y-arrow direction in FIG. 1).

As shown in FIG. 1, the optical fiber ribbon 1 is composed of the noptical fibers 2 in total, and the adjacent two optical fibers 2 of then optical fibers 2 are intermittently connected together via theconnecting portions 3 in each of the ribbon longitudinal direction andthe ribbon width direction. The connecting portions 3 connecting theadjacent two optical fibers 2 together are formed in the ribbonlongitudinal direction at a fixed pitch P1, and have a shorter lengththan unconnected portions each located therebetween. Namely, the lengthof each connecting portion 3 is shorter than that of each unconnectedportion in the ribbon longitudinal direction.

Further, only one connecting portion 3 is formed in the ribbon widthdirection to connect the adjacent two optical fibers 2. The connectingportion 3 is not located on the same line in the ribbon width directionas the other connecting portion 3 connecting other adjacent two opticalfibers 2 but located in the offset position from the other connectingportion 3 in the ribbon longitudinal direction. Therefore, theconnecting portions 3 formed in the optical fiber ribbon 1 are arrangedin a zigzag manner as a whole. Note that the arrangement of theconnecting portions 3 is not limited to that shown in FIG. 1 and may beother configurations. The arrangement shown in FIG. 1 is merely anexample. Here, in addition to the arrangement in which only oneconnecting portion 3 is provided in the ribbon width direction, two ormore connecting portions 3 may be formed in the ribbon width directionin a manner such that at least one unconnected portion is locatedbetween the connecting portions 3

As shown in FIG. 2(A), the connecting portion 3 connects the adjacenttwo optical fibers 2 together in such a manner as to fill the gap Sbetween the adjacent two optical fibers 2 with resin (for example,ultraviolet curable resin) and then cure it. Both surfaces 3 a and 3 bof the connecting portion 3 are respectively positioned on the samelines as lines 4 and 5 each connecting the contact points of therespective optical fibers 2 when being placed on the horizontal surface.Therefore, the inner half circumferences of the optical fibers 2 facingthe gap S are covered with the resin composing the connecting portion 3,but the outer half circumferences on the opposite side of the gap S arenot covered with the resin.

The two surfaces 3 a and 3 b of the connecting portion 3 shown in FIG.2(B) are each formed into a recess having a concave shape curved towardthe center of the gap S to separate from the lines 4 and 5 eachconnecting the contact points of the respective optical fibers 2 whenbeing placed on the horizontal surface. In FIG. 2(B), the amount of theresin composing the connecting portion 3 is smaller than that in FIG.2(A), and the resin is locally concentrated in the central portion ofthe gap S between the two optical fibers 2. The optical fiber ribbonconnected with the connecting portions 3 having such a configuration ismore easily bent since the amount of the resin used is smaller than thatof the connecting portion 3 shown in FIG. 2(A), so that the number ofthe optical fiber ribbons to be housed in a cable further increases.

Each of the optical fibers 2 includes a bare glass optical fiber 6provided in the center thereof, a first cover layer 7 covering theperiphery of the glass optical fiber 6, and a second cover layer 8further covering the periphery of the first cover layer 7. The glassoptical fiber 6 has a diameter of 125 μm. The first cover layer 7 is arelatively soft resin layer to absorb lateral pressure applied to theglass. The second cover layer 8 is a relatively hard resin layer toprotect against external damage. The second cover layer 8 may be furthercovered with a colored layer so that the respective optical fibers 2 canbe discriminated therebetween. The colored layer is formed as anoutermost layer so as to easily differentiate the respective opticalfibers 2 visually.

According to the present embodiment, the outer diameter dimension of theoptical fibers 2 (the entire diameter including the outermost layer) His set to smaller than or equal to 220 μm, and the distance L betweenthe centers of the adjacent two optical fibers 2 is set to 250±30 μm.The optical fiber 2 of the present embodiment is a size smaller than theoptical fiber 2 conventionally used which has the outer diameterdimension H of 250 μm. In addition, the distance L between the centersof the adjacent two optical fibers in the optical fiber ribbonconventionally used is 250 μm. The present embodiment sets the distanceL to 250 μm with a margin of plus or minus 30 μm.

The connecting portion 3 shown in FIG. 2(A) has a thickness which is thesame as the outer diameter dimension H of the optical fibers 2. Theconnecting portion 3 shown in FIG. 2(B) has a thickness which is smallerthan the outer diameter dimension H of the optical fibers 2.

The optical fiber ribbon 1 has an intermittent fixing structure in whichthe connecting portions 3 are intermittently provided in each of theribbon longitudinal direction and the ribbon width direction to connectthe adjacent two optical fibers 2 together, and has a configuration inwhich the optical fibers 2 have the outer diameter dimension H ofsmaller than or equal to 220 μm which is smaller than that of theconventionally-used optical fibers, which contributes to decreasing thediameter of the optical fibers 2 and easily bending the ribbon. As aresult, a larger number of the optical fiber ribbons 1 can be housed ina cable compared with optical fiber ribbons having a conventionalstructure so as to increase the packaging density thereof.

Further, since the optical fiber ribbon according to the presentembodiment has a configuration in which the optical fibers 2 have theouter diameter dimension H of smaller than or equal to 220 μm which issmaller than that of the conventionally-used optical fibers, the volumeof the optical fibers can be reduced by 20% or greater compared with theoptical fibers having a conventional configuration. Accordingly, theentire diameter of the optical fiber ribbon can be decreased so as tofurther increase the packaging density thereof.

It should be noted that the connecting portions 3 are not limited to theconfigurations shown in FIG. 2(A) and FIG. 2(B) in which the connectingportions 3 are formed only in the gap S between the adjacent two opticalfibers 2, but may have the configurations shown in FIG. 3(A) and FIG.3(B). The connecting portions 3 shown in FIG. 3 are formed in such amanner as to fill resin into the gap S between the adjacent two opticalfibers 2 and cover the peripheries of the optical fibers 2 with theresin. The resin thickness T on the outer half circumference of eachoptical fiber 2 covered with the connecting portion 3 is set to smallerthan or equal to 15 μm.

The example shown in FIG. 3, in which the outer half circumference ofeach optical fiber 2 having the outer diameter dimension of 220 μm iscovered with the resin, has no influence on the bending performance ofthe optical fiber ribbon 1 since the resin thickness T of the resincovering the outer half circumference is as thin as 15 μm or smaller.Therefore, such a configuration does not prevent from improving thepackaging density in the cable.

EXAMPLE

Several types of optical fibers having different outer diameterdimensions were used in which the distance between the centers ofadjacent optical fibers varied, so as to manufacture optical fiberribbons (4-core ribbons). The manufacture of connecting portions andunconnected portions employed the method disclosed in JapaneseUnexamined Patent Application Publication No. 2010-033010 (JapanesePatent Application No. 2009-082778). The pitch adjustment between theoptical fibers employed the method disclosed in Japanese UnexaminedPatent Application Publication No. 08-146239 (Japanese PatentApplication No. 06-163292). Note that all optical fibers in one opticalfiber ribbon have the same outer diameter dimension.

Next, batch fusion splicing performance was evaluated when one opticalfiber ribbon thus obtained was entirely fused with the other opticalfiber ribbon. The operation process was as follows. First, the opticalfiber ribbon was held with a holder, the first cover layers 7 and thesecond cover layers 8 covering the respective optical fibers wereremoved by use of Hot Jacket Stripper to obtain the bare glass opticalfibers 6, and side surfaces of the bare glass optical fibers 6 thusobtained were cut with a fiber cutter. Subsequently, the respectiveglass optical fibers 6 in the optical fiber ribbon held with the holderwere placed on a fusion machine 10 having V-shaped grooves 9 formed at afixed pitch P2 shown in FIG. 4. In this state, the evaluation wasperformed in such a manner as to determine whether the respective glassoptical fibers 6 were placed in the corresponding V-shaped grooves 9.The case where the glass optical fibers 6 were placed in the V-shapedgrooves 9 was defined as OK, and the case where the glass optical fibers6 deviated from the V-shaped grooves 9 was defined as NG.

Hot Jacket Stripper used was HJS-02 manufactured by Fujikura Ltd. Thefiber cutter used was CT-30 manufactured by Fujikura Ltd. The fusionmachine used was FSM-60R also manufactured by Fujikura Ltd. The pitch P2between the respective V-shaped grooves 9 in the fusion machine 10 is250 μm. The operation under the conditions described above was repeated10 times and the number of NG was then counted. Table 1 shows theevaluation thereof.

TABLE 1 Outer Diameter of Distance between Centers of Number of NG inOptical Fiber Adjacent Optical Fibers Batch Fusion Splicing (μm) (μm)Performance 220 300 8 220 280 0 220 250 0 220 230 0 200 280 0 200 250 0200 220 0 180 300 6 180 280 0 180 250 0 180 220 0 180 200 4

The results shown in Table 1 revealed that, when the distance L betweenthe centers of the adjacent optical fibers 2 of the optical fiber ribbon1 having an intermittent fixing structure is set to 250±30 μm (220 μm to280 μm), the glass optical fibers 6 do not deviate from the V-shapedgrooves 9 so as to be concurrently fused with the corresponding glassoptical fibers of the other optical fiber ribbon. The number of NGincreased when the optical fiber ribbon did not meet the above-describedcondition, and the glass optical fibers 6 could not be placed in theV-shaped grooves 9 precisely.

[Optical Fiber Cable]

FIG. 5 shows an example of a center tube-type optical fiber cablehousing the optical fiber ribbon according to the present embodimenttherein. The center tube-type optical fiber cable 11 has a configurationin which the optical fiber ribbon 1 of the present embodiment is formedinto a cable core 12 in a manner such that the optical fibers 2 arerolled in the ribbon width direction and assembled into a bundle asindicated by a dashed and double-dotted line in FIG. 5, thermoplasticresin is extruded over the periphery of the cable core 12 thus obtainedso as to form a tube 13 thereon, and the tube 13 is further covered withpolyethylene so as to form a sheath 14 thereon.

FIG. 6 shows an example of an SZ-slotted optical fiber cable housing theoptical fiber ribbon according to the present embodiment therein. TheSZ-slotted optical fiber cable 15 has a configuration in which aplurality of slots 18 having a U-shape in cross section are formed onthe outer periphery of a slot core 17 including a tension member 16 inthe center thereof extending in the ribbon longitudinal direction, theoptical fiber ribbon 1 according to the present embodiment is rolled inthe ribbon width direction into a bundle and housed in each of the slots18, the peripheral surface of the slot core 17 including the openings ofthe slots 18 is covered with a press winding tape 19, and a sheath 20 isfurther formed thereon by extrusion.

FIG. 7 shows an example of a C-slotted optical fiber cable housing theoptical fiber ribbon according to the present embodiment therein. TheC-slotted optical fiber cable 21 has a configuration in which theoptical fiber ribbon 1 according to the present embodiment is rolled inthe ribbon width direction into a bundle and housed in a slot groove 24of a slot core 23 having a C-shape in cross section including tensionmembers 22 therein, and the entire slot core is covered with a sheath 26via a press winding tape 25 interposed therebetween.

Although the optical fiber ribbon 1 shown in each of FIG. 5, FIG. 6 andFIG. 7 according to the present embodiment is rolled in the ribbon widthdirection into a bundle and housed in the cable, the optical fiberribbon 1 according to the present embodiment may be folded in layers inthe vertical direction and housed in the cable. Alternatively, aplurality of the optical fiber ribbons 1 may be stacked on top of oneanother to have a stacked structure and then housed in the cable.

The optical fiber cables 11, 15 and 21 according to the presentembodiment each use the optical fibers 2 having the reduced outerdiameter dimension of smaller than or equal to 220 μm. Therefore, alarger number of the optical fibers 2 can be housed in the cable,compared with the conventionally-used optical fibers 2 having the outerdiameter dimension of 250 μm, so as to ensure higher density. Further,the optical fiber cables 11, 15 and 21 according to the presentembodiment can house the optical fiber ribbon 1 having an intermittentfixing structure in any state in a manner such that the optical fiberribbon 1 is bent and rolled into a cylindrical shape or folded to bestacked in any direction.

Further, the optical fiber cables 11, 15 and 21 according to the presentembodiment can easily separate the respective optical fibers 2 from eachother so as to improve single-core separation workability at the time ofterminal leading to extract the optical fibers 2 from the terminals ofthe cable or at the time of connecting operation to connect a connectorto the extracted optical fibers 2, since the optical fiber cables 11, 15and 21 each use the optical fiber ribbon 1 including the connectingportions 3 intermittently formed in each of the ribbon longitudinaldirection and the ribbon width direction to connect the adjacent twooptical fibers 2 together.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the optical fiber ribbon havingan intermittent fixing structure to intermittently connect the adjacentoptical fibers together via the connecting portions.

1. An optical fiber ribbon comprising three or more of optical fibersarranged in parallel and connecting portions connecting adjacent twooptical fibers together, the connecting portions being intermittentlyprovided in each of a ribbon longitudinal direction and a ribbon widthdirection, wherein a gap is formed between adjacent two optical fibers,the connecting portions are each formed in such a manner as to fillresin into the gap, and both surfaces of the respective connectingportions are each formed into a recess having a concave shape curvedtoward a center of the gap to separate from lines each connectingcontact points of the optical fibers when being placed on a horizontalsurface.
 2. The optical fiber ribbon according to claim 1, wherein anouter diameter dimension of the optical fibers is set to smaller than orequal to 220 μm, and a distance between centers of the adjacent twooptical fibers is set to 250 μm with a margin of plus or minus 30 μm. 3.The optical fiber ribbon according to claim 1, wherein an outermostlayer of the respective optical fibers is colored.
 4. An optical fibercable housing the optical fiber ribbon according to claim 1 therein. 5.An optical fiber ribbon comprising three or more of optical fibersarranged in parallel and connecting portions connecting adjacent twooptical fibers together, the connecting portions being intermittentlyprovided in each of a ribbon longitudinal direction and a ribbon widthdirection, wherein a gap if formed between adjacent two optical fibers,the connecting portions are each formed in such a manner as to fillresin into the gap and cover a periphery of the respective opticalfibers with the resin, and both surfaces of the respective connectingportions are each formed into a recess having a concave shape curvedtoward a center of the gap to separate from lines each connectingcontact points of the optical fibers when being placed on a horizontalsurface.
 6. The optical fiber ribbon according to claim 5, wherein anouter diameter dimension of the optical fibers is set to smaller than orequal to 220 μm, and a distance between centers of the adjacent twooptical fibers is set to 250 μm with a margin of plus or minus 30 μm. 7.The optical fiber ribbon according to claim 5, wherein a resin thicknessof the periphery covered with the resin is set to smaller than or equalto 15 μm.
 8. The optical fiber ribbon according to claim 5, wherein anoutermost layer of the respective optical fibers is colored.